Fill in missing dates for multiple values with a GROUP BY

Question

I'm trying to write a single query for retrieving time information for multiple users over a date range.

My tables are set up as follows:

Entry:

user_id  | entry_date  | entry_hours
1        | 2013-11-12  | 4
1        | 2013-11-12  | 5
1        | 2013-11-13  | 3
2        | 2013-11-13  | 7
....

Calendar:

calendar_date
.....
2013-11-10
2013-11-11
2013-11-12
2013-11-13
2013-11-14
.....

If I run this query:

SELECT *, e.user_id, e.entry_date, COALESCE(SUM(e.entry_hours), 0) as total
            FROM `entry` e
            WHERE entry_date BETWEEN '2013-11-12' and '2013-11-13'
            GROUP BY e.user_id, e.entry_date

I get something to the effect of

user_id  |  entry_date  |  total
  1      |  2013-11-12  |  9
  1      |  2013-11-13  |  3
  2      |  2013-11-13  |  7

When I would like this instead:

user_id  |  entry_date  |  total
  1      |  2013-11-12  |  9
  1      |  2013-11-13  |  3
  2      |  2013-11-12  |  0
  2      |  2013-11-13  |  7

Where it fills in the missing date with a 0.

EDIT: I would also need it to pull in user_id's with 0's when they have no listed entries. Say I included in there WHERE clause AND user_id IN (1,2,3), I would get something like:

user_id  |  entry_date  |  total
  1      |  2013-11-12  |  9
  1      |  2013-11-13  |  3
  2      |  2013-11-12  |  0
  2      |  2013-11-13  |  7
  3      |  2013-11-12  |  0
  3      |  2013-11-13  |  0

The idea behind the calendar table was to be able to pull all dates in a range and join them with the entry table to fill in those missing dates, but I've been unable to figure out how to do this.

Can anyone point me in the right direction?

Answer 1

SELECT
  u.user_id,
  c.calendar_date,
  COALESCE(SUM(e.entry_hours), 0)
FROM calendar c
CROSS JOIN users u
LEFT JOIN entry e
   ON (c.calendar_date = e.entry_date AND u.user_id = e.user_id)
GROUP BY u.user_id,c.calendar_date